When I was in charge of attorney development in my old law firm I was asked, how I knew when an associate was ready to be considered for partner. I answered that when an associate quits thinking like an employee and starts thinking like a partner he or she is ready. 
I recently read: The Impact Equation by Chris Brogan and Julien Smith.
In the book the authors write:
Owners, for example, search out opportunities, while employees wait for opportunities to come to them.
Isn’t that a good criteria to determine whether an associate is ready to be considered to become a partner? Suppose I asked you to finish this post by providing examples of how partners look for opportunities. What would be on your list?